docs: def pip_create_virtualenv(path=None):
      """Create an isolated Python environment."""
      if six.PY2:
          apt_install('python-virtualenv')
      else:
          apt_install('python3-virtualenv')
  
      if path:
          venv_path = path
      else:
          venv_path = os.path.join(charm_dir(), 'venv')
  
      if not os.path.exists(venv_path):
          subprocess.check_call(['virtualenv', venv_path])